JPH09218109A - Sensor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the continuous adhesion of a platinum resistor to a dielectric support layer even under room temperature, high temperature, and dry atmospheres, and high humidity atmosphere by arranging an adhesive layer formed of a specified silicide between a resistance element and the dielectric support layer. SOLUTION: A dielectric support layer 21 is formed of a silicon oxide thin film generated on a silicon plate, and an adhesive layer 22 formed of a silicide such as platinum silicide, molybdenum silicide, tungsten silicide, tantalum silicide, titanium silicide, or cobalt silicide is provided thereon. The adhesive layer 22 is covered with a resistance element platinum layer 23. A heating at high temperature is successively performed, whereby a platinum silicide layer is formed. Thus, stability can be kept even when the resulting resistance element is loaded to room temperature, high temperature and high humidity for a long time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor having a dielectric support layer on a resistance element made of platinum and a method for manufacturing the sensor.

[0002]

From EP 0 375 399 A1 a sensor is already known which has a microbridge in which a heating element made of platinum is arranged. Such a sensor is preferably used as a mass flow sensor.
In order to ensure a sufficiently good adhesion of the platinum layer structuring the heating element to the dielectric support layer, the metal oxides must be Pt and S.
It is used as an adhesion-mediating layer with I ₃ N ₄ .

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a sensor having a dielectric carrier on a resistance element made of platinum. It is an object of the present invention to provide a sensor that is guaranteed even in a high humidity atmosphere and a manufacturing method thereof.

[0004]

The above-mentioned problems are solved in the sensor described at the beginning, by using platinum silicide (P) between the resistance element and the film.
tSi ₂ ) or molybdenum silicide (MoSi ₂ ) or tungsten silicide (WSi ₂ ) or tantalum silicide (TaSi ₂ )
Or titanium silicide (TiSi ₂ ) or cobalt silicide (Co
This is solved by the fact that an adhesion layer made of Si ₂ ) is arranged.

Yet another object is to provide a method for manufacturing a sensor, which comprises coating a platinum layer on a dielectric support layer,
The solution is to apply between the platinum layer and the support layer a platinum silicide layer, or a silicon layer which is at least partially converted to platinum silicide in a subsequent heat treatment step.

Further, the above-mentioned problems are, in a method of manufacturing a sensor in which a gold layer is coated on a dielectric support layer, molybdenum silicide (MoSi ₂ ) or tungsten silicide (WSi ₂ ) or a tungsten silicide (WSi ₂ ) layer between the platinum layer and the support layer. Tantalum silicide (TaSi ₂ ) or titanium silicide (TiSi ₂ ) or cobalt silicide (CoS)
It is solved by applying i ₂ ).

The above-described sensor according to the invention and its manufacturing method achieve an improved adhesion of the platinum layer to the dielectric support layer compared to the prior art, the adhesion being clearly higher at room temperature. Maintains stability even when subjected to temperature (> 250 ° C) and high air humidity for a long time. Furthermore, the sensor according to the invention can be manufactured in a particularly simple manner.

Further, platinum silicide (PtSi ₂ ), molybdenum silicide (MoSi ₂ ), tungsten silicide (WSi ₂ ),
Tantalum silicide (TaSi ₂ ), titanium silicide (TiS
It has been found that the adhesion layer used, i ₂ ), cobalt silicide (CoSi ₂ ) does not influence the properties of the platinum layer, in particular the resistance as a function of temperature. Compared to complex coatings of metal oxides, adhesion layers made of metal silicides are particularly easy to produce.

According to an advantageous embodiment of the invention, silicon oxide, silicon nitride, silicon oxynitride or silicon carbide or a layer sequence of these materials is provided as material for the dielectric support layer.

According to another embodiment, the Pt resistance element is 1
Has a thickness of 0 to 200 nm, preferably 140 to 160 nm, and the platinum silicide layer is 2 to 8 nm, preferably 3 to 6 nm.
It has a thickness of nm.

According to another embodiment, a coating layer is provided to cover the upper surface of the support layer and the resistance element, and platinum silicide (PtSi ₂ ) or molybdenum silicide (MoSi) is provided between the resistance element and the coating layer. ₂ ) or tungsten silicide (W
An adhesion layer of Si ₂ ) or tantalum silicide (TaSi ₂ ) or titanium silicide (TiSi ₂ ) or cobalt silicide (CoSi ₂ ) is arranged.

According to a further embodiment, at least one temperature probe of platinum is arranged on the support layer.

According to a preferred embodiment of the method for manufacturing a sensor according to the invention, the platinum layer is structured, and according to another preferred embodiment, the support layer is formed by thermal oxidation of a silicon plate.

As the material for the support layer, which can form a closed film on the Si cavities, there are numerous materials containing silicon (SiO ₂ , Si ₃ N ₄ , S based on various coating methods).
i _x N _y, etc.) has been demonstrated to be suitable. A thin metal silicide layer has proved suitable as an adhesion layer between the support layer (membrane) and the platinum, in which only slight additional stresses due to heat penetrate. Typical dimensions of the platinum layer are 140-160 nm. The metal silicide layer is typically 3-6 nm thick. A dielectric cover layer may be provided to protect the heating element. In this case, an adhesion layer consisting of one of the abovementioned metal silicides is provided between the heating element and the covering layer.

[0015]

Next, the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 shows a sensor 1 in which the membrane 2 is stretched over a frame 3 of monocrystalline silicon. A heating element 4 is arranged on the membrane 2. Temperature probes 5 are arranged on both sides of the heating element 4. The heating element 4 and the temperature probe 5 are electrically connected to each other via a lead wire 6 arranged on the frame 4. The leads 6 end in connection areas 7 in which the connection wires for the contact of the heating element 4 and the temperature probe 5 can be attached. A cross-sectional view of the sensor 1 in the region of the membrane 2 is shown in FIG. As is apparent from the drawing, the dimensions of the frame 3 and the membrane 2 are determined by the notches 8 starting from the back side of the sensor 1 and extending to the membrane 2. In FIG. 2, the geometrical dimensions of the heating element 4 and the temperature probe 5 are exaggerated. Furthermore, another coating layer 9 is provided on the upper surface, which coating covers the upper surface of the membrane 2 and also the temperature probe 5.

The sensor shown in FIG. 2 is a mass flow sensor whose principle is known from EP-A-375399. The heating element 4 below the temperature probe 5 is a resistive element structured from a thin platinum layer. Heating element 4
A current is conducted therethrough, which heats the film around the heating element 4. The temperature of the film can be measured by measuring the electric resistance with the temperature probe 5. When the flow over the upper surface of such a sensor, in particular the air flow, is abraded, heat is taken from the membrane 2 by the associated mass flow. In this case, depending on the strength of the flow, the temperature of the membrane is reduced, in which case the temperature probes 5 arranged on either side of the heating element 4 display different temperature values depending on the flow direction.
Alternatively, it is also possible to provide only the heating element 4 on the membrane and to detect the mass flow in the measurement of the resistance of this heated element.

The sensor 1 is manufactured starting from a silicon plate having a film layer coated on its upper surface. The heating element 4 and the temperature probe 5 are manufactured by first coating a platinum layer on the entire surface of this film layer and structuring the platinum layer in a separate step. From the platinum layer, at the same time, it is also possible to structure the leads 6 and the connecting regions 7 which are distinguished from the heating element 4 and the temperature probe 5 by their width. Due to the large width of the leads, the resistance of these leads is significantly lower than that of the heating element 4 and the temperature probe 5. Then, if necessary, the coating layer 9 is applied. In the other step, a notch 8 is provided which extends from the back surface of the silicon wafer to the film 2. A large number of such sensors are manufactured on a single silicon plate, and the wafer is then cut into a large number of individual sensors 1.
Can be divided into

FIG. 3 shows an enlarged cross-sectional view of the film of the heating element 4. The film 2 is formed from the dielectric film layer 21. This dielectric film layer 21 may for example consist of silicon dioxide, silicon nitride, silicon oxynitride or silicon carbide (SiC) or a sandwich-like sequence of at least two of these layers. These materials are particularly suitable for films stretched over a frame of single crystal silicon. However, other materials are also suitable, for example ceramic materials or glass. However, preference is given to a layer arrangement with silicon oxide as the last layer, which can be produced on a silicon plate with particularly simple measures and with particularly good quality. On the film layer 21, platinum silicide (PtSi
₂ ) or molybdenum silicide (MoSi ₂ ), tungsten silicide (WSi ₂ ), tantalum silicide (TaSi ₂ ), titanium silicide (TiSi ₂ ), or cobalt silicide (CoSi ₂ ). Platinum silicide (Pt
Si ₂ ), molybdenum silicide (MoSi ₂ ), tungsten silicide (WSi ₂ ), tantalum silicide (TaSi ₂ ), titanium silicide (TiSi ₂ ), or cobalt silicide (CoSi ₂ ), and then a platinum layer. It is arranged. If desired, the heating element 4 and optionally the temperature probe 5 can also be coated. In this case, the covering layer is formed from the dielectric layer 25, which may optionally be platinum silicide (PtSi ₂ ) or molybdenum silicide (MoSi ₂ ) or tungsten silicide (WSi ₂ ) or tantalum silicide (dielectric layer 25). It is also possible to provide an adhesion-mediating layer 24 made of TaSi ₂ ) or titanium silicide (TiSi ₂ ) or cobalt silicide (CoSi ₂ ).

The present invention will now be described first with reference to the preferred embodiment of the platinum silicide layer. The silicon oxide layer 21 can be manufactured by thermal oxidation of the surface of a silicon plate, for example. Such a thermal oxide layer has a particularly high quality. The adhesion-mediating silicide layer 22 can be manufactured by first depositing a thin silicon layer on the silicon oxide layer 21. This deposition can be carried out, for example, by sputtering or evaporation with an electron beam or by chemical deposition from the gas phase. For chemical deposition, the deposition methods for polysilicon thin films known from semiconductor technology are suitable. The thickness of the silicon layer thus formed is a few nm, preferably 5 nm. Then, the platinum layer 23 is applied in another step. The platinum silicide layer is then formed by tempering, ie heating the layer to a temperature above 500 ° C. In this case, the initially coated silicon layer is converted to platinum silicide by reaction with the partially or completely coated platinum. Platinum layer 2
Since the layer thickness of 3 is greater than 100 nm, only a small portion of the coated platinum is consumed due to the formation of platinum silicide. Therefore, there is always an extra residual thickness of the platinum layer for the heating element or temperature probe. The conversion of the silicon layer into a platinum silicide layer can be carried out immediately after application of the platinum layer, after structuring of the platinum layer or after application of the coating layer. FIG. 3 shows another adhesion layer 24 of platinum silicide and a silicon oxide layer 25 which acts as a cover layer. The platinum silicide layer 24 is similarly formed by coating a thin silicon layer which reacts with the platinum material of the platinum layer 23. Alternatively, the platinum silicide layers 22 and 24 are applied by direct sputtering (sputtering of Pt-Si target, co-sputtering of Si and Pt or reactive sputtering of Pt in silane gas) or electron beam evaporation of platinum silicide. You can

The preferred production of the layer structure of FIG. 3 starts with the surface of the silicon wafer to be thermally oxidized grown to a layer thickness of the oxide of approximately 500 nm. Then, using a sputtering device, silicon 5 nm and platinum 150 nm on top of it
And 5 nm of silicon is sputter coated thereon. Subsequently, photoresist is applied, structured by lithography and finally the structure thus produced is converted by plasma etching into a layer structure consisting of an upper silicon layer, a platinum layer and a lower silicon layer. This conversion can be performed by, for example, a plasma etching method using ion beam etching. Then, in a separate step, a silicon oxide layer with a thickness of about 400 nm is produced by chemical vapor deposition, as is known from semiconductor technology. After that, a tempering step is carried out in which the layer arrangement is heated to a temperature above 500 ° C., preferably above 650 ° C. During this tempering process, the silicon layer is converted into a platinum silicide layer, in which case the platinum layer is consumed. Furthermore, the properties of the platinum layer are favorably influenced during this tempering process. In the measuring principle used for the sensor, it is desirable to adjust the temperature dependence of the resistance of the platinum layer as accurately and reproducibly as possible. This is achieved in the tempering process. Furthermore, the temperature coefficient of the resistance thus produced and the resistance itself are stabilized over a long period of time, that is to say the change of this temperature coefficient or the resistance over a long period (thousands of operating hours) is reduced. Is guaranteed. In this case, it has been experimentally found that platinum silicide has only a slight effect on the long-term stability of the properties of the platinum layer.

Furthermore, the lower layer 21 can use not only one material, but also different dielectric materials, for example a layer sequence consisting of one layer of silicon oxide and one layer of a nitride layer. is there.

Molybdenum silicide (MoSi ₂ ), tungsten silicide (WSi ₂ ), tantalum silicide (TaSi ₂ ), titanium silicide (TiSi ₂ ), or cobalt silicide (CoSi ₂ ).
The production of a sensor with Pt is carried out correspondingly to the production of a sensor with a platinum silicide layer, in which case only these thin layers can be converted into thin silicon layers by heating elements or temperature probes of platinum. They differ in that they cannot be formed. Therefore, these layers are applied by direct vapor deposition, sputtering or chemical deposition. It is particularly simple to manufacture by starting from a metal silicide target and applying a sputter coating. Compared to the platinum silicide layer, molybdenum silicide (MoSi ₂ ), tungsten silicide (WSi ₂ ), tantalum silicide (TaSi ₂ ), titanium silicide (TiSi ₂ ), and cobalt silicide (CoSi ₂ ) make the sensor 1300.
It has the advantage of extremely high temperature stability so that it can be heat treated to high temperatures up to ° C. In this case, care must be taken not to cause silicon diffusion in the platinum layer, which can deteriorate the temperature dependence of the electrical resistance in the platinum layer.

[Brief description of drawings]

FIG. 1 is a plan view of a sensor according to the present invention.

FIG. 2 is a cross-sectional view of a sensor according to the present invention.

FIG. 3 is an enlarged cross-sectional view of a film according to the present invention.

[Explanation of symbols]

2 support layer (film), 4 resistance element, 9,25 coating layer, 21 dielectric support layer, 22 platinum silicide layer, 2
3 Platinum layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Christoph Troitler, Federal Republic of Germany Van Weil Georg Strasse 1 (72) Inventor Michael Gundlach, Germany Asperk Eberhard Strasse 3-1 (72) Inventor Manfred Melendorf, German Federation Republic Leonberg Ludwig-Fink-Wake 23 (72) Inventor Steffen Schmidt Germany Reutlingen Holbeinstraße 75 (72) Inventor Franz Lermer Germany Stuttgart Vitikovek 9 (72) Inventor Christoph Kampshof German Reutlingen Nova Lisv Over click 1 (72) inventor Klaus Haiasu Germany Reutlingen low belt - Koch Strasse 37 (72) inventor Jörg boot Germany Geruringen Obe les Ringstrasse 7

Claims (9)

[Claims] 1. A sensor having a dielectric support layer (2) in which a resistance element (4) made of platinum is arranged, wherein platinum silicide (PtSi ₂ ) or platinum silicide (PtSi ₂ ) is provided between the resistance element (4) and the film (2). An adhesive layer (22) made of molybdenum silicide (MoSi ₂ ) or tungsten silicide (WSi ₂ ) or tantalum silicide (TaSi ₂ ) or titanium silicide (TiSi ₂ ) or cobalt silicide (CoSi ₂ ) is arranged. Sensor to do. 2. The sensor according to claim 1, wherein silicon oxide, silicon nitride, silicon oxynitride or silicon carbide or a layer sequence of these materials is provided as material for the dielectric support layer. 3. The Pt resistance element (4) is 100 to 200 n
A sensor according to claim 1 or 2, having a thickness of m and the platinum silicide layer having a thickness of 2-8 nm. 4. The upper surface of the support layer (2) and the resistance element (4)
Is provided, and platinum silicide (PtSi) is provided between the resistance element (4) and the coating layers (9, 25).
₂ ) or molybdenum silicide (MoSi ₂ ) or tungsten silicide (WSi ₂ ) or tantalum silicide (TaSi ₂ ) or titanium silicide (TiSi ₂ ) or cobalt silicide (CoSi ₂ )
Sensor according to any one of claims 1 to 3, wherein an adhesion layer (24) consisting of is arranged. 5. Sensor according to claim 1, wherein at least one temperature probe (5) made of platinum is arranged on the support layer (2). 6. The platinum layer (23) is replaced by a dielectric support layer (21).
A method for manufacturing a sensor coated on a platinum layer (2
3) A method for manufacturing a sensor, characterized in that a platinum silicide layer (22) or a silicon layer which is at least partially converted to platinum silicide in a subsequent heat treatment step is applied between the support layer (21) and the support layer (21). . 7. A method for manufacturing a sensor, wherein a gold layer (23) is coated on a dielectric support layer (21), the platinum layer (2
3) between the support layer (21) and molybdenum silicide (MoSi)
₂ ) or tungsten silicide (WSi ₂ ), tantalum silicide (TaSi ₂ ), titanium silicide (TiSi ₂ ), or cobalt silicide (CoSi ₂ ) is applied. 8. The method according to claim 6, wherein the platinum layer (23) is structured. 9. The method according to claim 6, wherein the support layer (21) is formed by thermal oxidation of a silicon plate.